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    Re: The Star of Bethlehem and Navigation
    From: Frank Reed
    Date: 2009 Jan 5, 16:59 -0800

    Mike Dorl, you wrote:
    "I start up my almanac program and put in the lat/log of Ugarit (35.8E 
    35.683N), set the date to 3/5/1223 BC and play with the time until I get 
    the lunar distance of the sun as low as possible at 1152.  I then have a 
    separation of 4' 9.3".  I diddle delta T which my program has set to 
    28404.763 and find I can get a closer approach at 11:50 with a delta T 
    of 28460.000.
    
    So what am doing when I diddle delta T?
    
    The picture I have in my mind is a sphere with the path of the eclipse 
    outlined on it with an overlay sphere with a map of the world on it.  So 
    by changing delta T I  revolve the map about the earths axis  relative 
    to first sphere to bring Ugarit closer to the center of  the path of the 
    eclipse.   So delta T is constrained to those values which bring Ugarit 
    into the path of the eclipse.
    
    Is that an ok way to think about it? "
    
    That's just how I think about it. So you would want to adjust delta-T until 
    Ugarit is on the east and then again on the west limits of the total eclipse 
    path. Those would then be good limits on delta-T for that date. All of this 
    assumes that the brief description on the tablet actually refers to a total 
    eclipse, and the eclipse was seen at Ugarit exactly and not at some nearby 
    place.
    
    And you wrote:
    "Hopefully my almanac has also made some reasonable adjustments for 
    changes in the earths axis.  Are those know well enough and predictable 
    enough to project them 3000 years into the past?"
    
    The change in inclination shouldn't be a problem for historical dates. Things 
    only get complicated, in my experience, when you deal with time periods of 
    tens of thousands of years.
    
    -FER
    
    
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